The invention concerns a refractory material based on chromium corundum, a chromium corundum brick made of said material as well as the use thereof.
Refractory materials based on chromium corundum comprising about 10% by wt. Cr2O3 and about 90% by wt. Al2O3 are known from Schulle, xe2x80x9cFeuerfeste Werkstoffexe2x80x9d, 1st edition, 1990 (ISBN 3-342-00306-5), pages 288, 289. There, refractory materials based on Cr2O3/ZrO2 are mentioned as well. At the same place it is indicated that the use of such materials as refractory ceramics is little known.
In EP 0 242 769 A2, a dense ceramic brick is described, which may consist of 10 to 90% by wt. of Al2O3, 90 to 10% by wt. of Cr2O3 and 0 to 40% by wt. of ZrO2, wherein the brick shall have a density of at least 92% of its theoretical density. Accordingly, the said oxides are used only in fine grain fractions ( less than 50 xcexcm). Such bricks are used in glass-melting furnaces, among other things.
Because of their high density, the known bricks are relatively brittle and show an unsatisfactory corrosion behavior, in particular at increased application temperatures (above 1,500xc2x0 C.).
Therefore, they cannot be applied, for example, in rotary kilns, as used in incinerating refuse, particularly in incinerating hazardous waste.
Thus, the object of the invention is to provide a refractory material and an associated brick, which are applicable in slag-carrying furnaces with high thermal cycling and high temperatures of operation (up to 1,650xc2x0 C.). Also, a structural elasticity as high as possible is to be obtained.
The invention has understood that materials based on chromium corundum can meet those requirements. For that, it is necessary to adapt the amounts of chromium oxide and corundum as well as the particle size of the selected raw materials.
In its most general embodiment, the invention accordingly concerns a refractory material based on chromium corundum, comprising:
5 to 35% by wt., preferably 10 to 30% by wt. of Cr2O3 having a particle size  less than 0.1 mm,
1 to 10% by wt., preferably 3 to 6% by wt. zirconia having a particle size between 0.5 and 4.0 mm,
55 to 94% by wt., preferably 62 to 87% by wt. alumina (corundum:) having a particle size between 0.2 and 4.0 mm.
Such a material based on chromium corundum can be manufactured to bricks having a high structural elasticity, which are suitable for the ranges of application mentioned above, for example rotary kilns for incinerating hazardous waste at temperatures of operation up to 1,700xc2x0 C.
The chromium oxide portion should have a particle size as fine as possible, therefore, according to an embodiment, a particle size of  less than 0.05 mm ( less than 50 xcexcm) is proposed.
The portion of zirconia may substantially consist of baddeleyite, wherein corresponding medium-grained to coarse-grained raw materials of baddeleyite may be used as baddeleyite support, for example sintered zirconium mullite, fused zirconium mullite, sintered zirconium corundum and fused zirconium corundum, alone or in mixture.
The content of ZrO2 affects substantially the structural elasticity and thus the temperature cycle resistance.
As far as raw materials containing corundum are used for the zirconia portion, the corresponding corundum portion is to be counted in the corundum component mentioned above (55 to 94% by wt. of the total mixture).
According to an embodiment, the refractory material may have an SiO2 portion of  less than 3% by wt. For example, mullite may be used as a raw material for said SiO2 portion.
As far as the zirconium mullite mentioned above is used as a ZrO2 raw material, here too the portion of mullite may be counted, proportionally, if necessary, in the SiO2 component.
For example, the corundum matrix consists of sintered corundum, fused corundum or mixtures thereof.
The said refractory material may be manufactured to bricks. The bricks may be pressed or stamped. They are fired at temperatures between 1,450 and 1,700xc2x0 C.
The specific particle structure of the individual material components as well as the addition of ZrO2 (baddeleyite) are substantially responsible for the high temperature cycle resistance and the low modulus of elasticity of such a brick.
By a corresponding selection of the raw materials as well as a coordination of the constituent amounts of Cr2O3, ZrO2 and Al2O3 and optionally SiO2 and Fe2O3 (the portion of Fe2O3 should be  less than 0.5% by wt.) as well as the maintenance of the particle sizes mentioned above for the individual material components a chromium corundum brick may be produced after firing at 1.450 to 1.700xc2x0 C., which has an open porosity between 9 and 18% by vol. and a modulus of elasticity  less than 30,000 N/mm2.
Here, the modulus of elasticity may be reduced to values up to 15,000 N/mm2 by correspondingly adapting the parameters mentioned above.
The temperature cycling stress (measured according to DIN EN 993, part 11) leads to a value  greater than 30.
The corrosion resistance of said bricks is well.
The chromium corundum brick as described above can be used to advantage in rotary kilns for incinerating refuse, in particular for incinerating hazardous waste. It is resistant up to temperatures of 1,700xc2x0 C. without loosing its high structural elasticity and its excellent corrosion behavior.
Further characteristics of the invention follow from the features of the subclaims as well as the other application documents.